A preferred servo-valve is shown and described in detail in U.S. Pat. No. 3,549,281 which also shows in section a variable displacement vane pump and the two pistons and biasing spring which adjust the position of an outer ring and the displacement of the pump. My copending application Ser. No. 078,332 and filed Sept. 24, 1979 for Servo-Valve Convertible Construction provides a flow control device optionally to be added to such a valve to convert the servo-valve to a load sensing valve which responds to the rate of flow of the pump output rather than pump output pressure. It is an object of the present invention to provide for the convenient and optional further addition of a displacement and torque limiting control which is directly responsive to the position of the pump displacement control means.